jQuery 1.2.6 was released recently, with plenty of bug-fixes and speed improvements. Most notably event handling was sped up 103% and the dimensions plugin was integrated into the framework (the dimensions plugin is an API to calculate elements sizes in a cross-browser and reliable way).

In addition, jQuery UI has recently reached release-candidate status, which means all non minor or trivial issues were solved and it's getting to the point that it will production ready shortly. I have been using its components for a while in anticipation of such release, and hopefully they will have their documentation up soon.